1. Field of the Invention
Embodiments of the present invention relate to a nonvolatile memory device made of resistance material and a method of fabricating the same, and more particularly, to a nonvolatile memory device capable of providing high integration and reducing a reset current and a method of fabricating the same.
2. Description of the Related Art
Ferroelectric RAM (FRAM), magnetic RAM (MRAM) and phase-change RAM (PRAM) are nonvolatile memory devices made of resistance material. While DRAM or flash memory stores binary data using charges, FRAM, MRAM and PRAM store binary data using a polarization characteristic of a ferroelectric material, a resistance change of a magnetic tunnel junction (MTJ) thin film based on magnetic properties of ferromagnets, and a resistance change due to a phase change, respectively. Since they have the high integration characteristics of DRAM and nonvolatile characteristics of flash memory, FRAM, MRAM and PRAM are considered to be alternatives to conventional volatile or nonvolatile memory devices.
As one of the nonvolatile memory devices using a resistance material, the PRAM stores binary data using properties displayed by phase-change materials such as GeSbTe (GST). These materials can switch between a crystalline state and an amorphous state due to local heat generated by electric pulses. A memory cell of the PRAM comprise a phase-change layer, a resistor, and a switching transistor. Generally, the transistor is formed on a silicon wafer, and the resistor and the phase-change layer are formed on the transistor. The phase-change layer is generally a GST base material called chalcogenide. The resistor is used to heat the phase-change layer. The phase-change layer changes between a crystalline state and an amorphous state depending on a degree of heat, resulting in a change of resistance. Since the current flowing through the resistor is proportional to a voltage, binary data can be stored and read.
Meanwhile, the resistance materials of conventional nonvolatile memory devices have good etching resistance. Thus, when using a conventional DRAM process, it is difficult to etch the resistor and, even though this is possible, it takes a long time to etch the resistor. For these reasons, conventional nonvolatile memory devices have reduced productivity, increased manufacturing costs and as a result are uncompetitive in markets. Accordingly, new resistance materials are increasingly in demand.
Also, since the resistors of the conventional nonvolatile memory devices are formed of a thin film type using physical vapor deposition (PVD), it is difficult to obtain a dense and uniform layer quality. It is also difficult to control a composition ratio of elements constituting the resistors, which can have a great influence on the switching characteristics of the memory devices.
A method of depositing metal oxide using an MOCVD method is disclosed in a Korean Patent Laid-Open Publication No. 2004-0055594. This publication discloses a technology of forming a metal-containing layer using a precursor. Meanwhile, an oxygen content of the metal-containing layer influences a switching characteristic of the memory device. The MOCVD method has a limitation in controlling the oxygen content. Also, since the metal-containing layer has a thin film shape, the high integration potential and reduction of reset current ability are limited. Accordingly, there is a demand for a memory device structure that can provide high integration and reduction of reset current.